Method of insulating electrical conductors

ABSTRACT

In electrical apparatus subject to nuclear radiation, electrical conductors, in particular for the magnet coils of an accelerator, are mechanically supported and electrically insulated from one another by concrete held under permanent compressive stress.

United States Patent Sheldon etal. [451 Apr. 18,1972

[54] METHOD OF INSULATING 2.911.572 11/1959 Francis ..29/624 ELECTRICAL CONDUCTORS 2,915,686 12/1959 Schuber1..... ..29/024 1721 kobenshewo-wbingdomcewwM Z'lifijiii 311323 3112??".... ...1..... ..1..IIIIIIiiI1 Stapleton, Wantage, both of England [73] Assignee: Science Research Council, London, En-

gland [22] Filed: June 9, 1969 [21] App]. No.: 831,306

[30] Foreign Application Priority Data June 12, 1968 Great Britain ..28,048/68 Jan. 31, 1969 Great Britain ..5,502/69 [52] U.S. Cl ..29/ 624 [51] Int. Cl ....l-l01b 13/00, l-l05k 3/00 [58] Field of Search ..29/624 [56] References Cited UNIT ED STATES PATENTS 2,590,821 3 /1952 l(iser.... H

Primary Examiner-John F. Campbell Assistant Examiner-Donald P. Rooney Attorney-Larson, Taylor and Hinds ABSTRACT o iYs i e e 7 Claims, 4 Drawing Figures 1 METHOD OF INSULATING ELECTRICAL CONDUCTORS The invention relates to the insulation of electrical conductors and more particularly to the insulation and mechanical support of electrical conductors.

The invention provides a method of manufacturing an electrical apparatus comprising supporting an electrical conductor or electrical conductors in a mould in the desired configuration for carrying electrical current when incorporated in the apparatus, and introducing concrete into the mould so as to embed the electrical conductor or conductors in concrete, reinforcement means being provided and arranged for permanently compressively stressing the concrete.

It is an important feature of the invention that the stress applied to the concrete is such as to minimize the effect of the differential in temperature coefficients of expansion between the concrete and the electrical conductor or conductors.

For this, the reinforcement means is preferably arranged so as to maintain the concrete under volume compression. The reinforcement means may comprise a vessel enclosing that portion of the electrical conductors which is to be supported in and insulated by concrete, the concrete being introduced, e.g. by pumping, into the vessel and pressurised, the pressure being maintained until the concrete has set. In that case, it will be appreciated that the mould is comprised by the reinforcement means.

Alternatively, the reinforcement means may comprise reinforcement members which extend through the mould and which are arranged to be tensioned so as to compressively stress the concrete when set. If volume compressive stress is not secured, it is desirable that the compressive stress should be, so far as is possible, parallel with the length of the electrical conductor or conductors.

The invention includes an electrical apparatus made by the aforesaid method.

The invention is especially applicable to installations subject to nuclear radiation where use of organic material in the insulation of electrical conductors is undesirable because of its liability to failure as a result of radiation damage.

The invention includes an installation subject to nuclear radiation wherein electrical conductors are insulated by a cladding of inorganic cementatious material. The electrical conductors may be encapsulated in an aggregate filled concrete.

The invention also provides an electrical installation subject to nuclear radiation wherein electrical conductors are embedded in concrete which provides mechanical support for the conductors and the electrical insulation, preferably the sole electrical insulation, between adjacent conductors, and which is so stressed as to minimize the effect of the differential in temperature coefficients of expansion between the concrete and the electrical conductors.

The invention also provides a method of manufacturing an electromagnet in an electrical machine for accelerating charged particles, which method comprises supporting in a mould in the required relative locations a beam tube, magnet core laminations and electrical coil windings of uninsulated electrical conductor, and embedding these components in concrete, reinforcement means being provided and arranged to permanently compressively stress the concrete to avoid or reduce the effects of the differential coefficient of expansion with temperature between the concrete and the electrical conductors.

Specific constructions of apparatus subject to nuclear radiation and methods of manufacture embodying the invention will now be described by way of example and with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic longitudinal section of part of an installation,

FIG. 2 is a diagrammatic section on line 2-2 of FIG. 1, with some parts omitted,

FIG. 3 is a fragmentary perspective view of part of the installation of FIGS. 1 and 2, and

FIG. 4 is a diagrammatic cross-sectional view of another installation.

In the example of FIGS. 1 to 3, the apparatus is an electrical machine for accelerating charged particles and the drawings illustrate the construction of a large electromagnet around the stainless steel beam tube 11.

The electromagnet comprises a yoke of laminated structure formed in two halves 12, 13 and coil windings 14 of copper, which have central passages 14a therethrough for cooling fluid.

The beam tube 11 extends centrally through the yoke 12, 13. The copper windings 14 extend through rectangular passages l5, 16 in the yoke on each side of the beam tube 11. The windings 14 are formed in two halves. In one-half, the windings 14 extend through passage 15 parallel with the beam tube 11, loop over the beam tube 11, extend through passage 16 parallel with the beam tube 11, loop over the beam tube 11 and extend through passage 15 again, and so on. In the other half, the windings 14 follow a similar path but loop under the beam tube 11 at each end of the passages 15 and 16.

To construct the electromagnet a former is made in which the beam tube 11 extends through central apertures in spaced steel plates 17, 18. Reinforcement rods 19, 21 with threaded ends are positioned so as to extend through apertures in the plates 17, 18. The number of reinforcement rods employed will depend upon the size of the magnet. For example, in a large magnet there will be at least eight reinforcement rods equispaced around the beam tube 11.

The windings 14, in this example, are separated and located with sintered alumina slips 22, not shown in FIGS. 1 and 2 but illustrated in FIG. 3. The windings l4 and beam tube 11 are assembled in position in the yoke 12, 13. The alumina slips 22 serve to support the windings 14 spaced from one another and from the yoke 12, 13 and from the beam tube 11.

Tension is applied to the reinforcement rods 19, 21 from an external structure (not shown). The whole structure is then encased to form a mould of which the steel plates l7, 18 form two side walls.

Concrete is introduced into the mould in stages and compacted so as to fill the interstices between the windings 11 and within the core structure 12, 13. This compaction is achieved for example by vibration and/or by the application of a vacuum to the enclosure formed by the mould. Alternatively, the concrete may be introduced by pumping and applying pressure, either directly, by means of the pump, or by separate application of pressure, e.g. hydraulically.

In this filling operation it may be appropriate to delay positioning the upper half 12 of the core structure until after some concrete has been introduced into the mould.

If it is desired to secure adhesion between the concrete and the copper windings l4, adhesion may be improved by shot blasting the windings 14 prior to encapsulation. Further improvement of adhesion may be achieved by coating the copper, for example by flame spraying, with alumina or other suitable ceramic material.

After the concrete has set, compressive stress upon the concrete, derived from the tension in the reinforcement rods 19, 21 is applied to the concrete by screwing nuts 22, 23, 24, 25 onto the threaded ends of the rods 19, 21 and releasing the externally applied tension. Tension in the rods 19, 21 then applies compression onto the concrete via the steel plates 17, 18. This compression is arranged to be such as to minimize the effects of the differential coefficient of expansion with temperature between the concrete and the copper.

In the example shown in FIG. 4, the assembly of laminations 31, 32 forming the yoke, beam tube 33 and windings 34 is closely similar to that of FIGS. 1 to 3.

However, in the example of FIG. 4, this assembly is supported, on lugs 35, centrally within a steel tube 36. The ends of the tube 36 are sealed and concrete 37 is pumped into the enclosure thus formed. Pressure is applied, either by the pump or separately-e.g. hydraulically, and the pressure is maintained until the concrete has set.

It will be appreciated that the application of pressure expands the tube 36 and, when the externally applied pressure is released after the concrete has set, the tube 36 will maintain a volume compressive stress upon the concrete 37.

ln FIG. 4, the tube 36 is illustrated as comprising two half tubes 38, 39 secured together by bolted flanges 41, 42. However, in certain circumstances, it may be preferable to employ an integral tube, the assembly of yoke, beam tube and windings being slid into position from an end of the tube.

A typical example of concrete used in the aforedescribed manufactures is as follows:

400 parts by weight aggregate 100 parts by weight calcium aluminate cement 40 parts water The aggregate comprised alumina particles of which 33% percent were in the size range 25 to 52 mesh and 66% percent were in the size range 14 to 25 mesh.

In each example, after setting, the concrete was cured at 150 C so as to achieve the desired electrical insulation properties of the concrete.

For improving the insulation properties without rendering the insulation liable to failure due to radiation damage, the alumina cement may have incorporated in it glass fibres, silica fibers or other inorganic fibrous or laminar materials such as asbestos or mica.

lt will be appreciated that in the apparatus of the aforedescribed examples extremely high accuracy of relative location of the components is required and has to be maintained under operating conditions which involve temperature cycling and exposure to intense nuclear radiation. The present invention is based upon the appreciation that concrete, which is resistant to damage by nuclear radiation, is capable of providing adequate electrical insulation and maintaining adequate spacial location of components, provided differential expansion and contraction of the concrete relative to the electrical conductors is kept low. This is achieved by arranging for the concrete to be maintained under permanent compression.

The insulation provided by the concrete is stable against ionising radiation, is cheap, and is resistant to high temperatures. The apparatus of the foregoing example may thus be employed in high vacuum applications. Further, the use of alumina cement is advantageous for the insulation and support of electrical apparatus for use at low temperatures, especially coils at 4.2 K, because the thermal conductivity of the concrete is much higher than that of conventional organic insulation.

The invention is not restricted to the details of the foregoing example. For instance, the method of manufacture described is especially suitable for magnet construction of large accelerators but is also likely to be useful in the construction of other apparatus or installations, in particular where subject to nuclear radiation, such as, for example, in thermonuclear reactors.

While the use of alumina cement is preferred, Portland cement or other suitable cement may be used if desired.

We claim:

1. A method of manufacturing an electrical apparatus comprising supporting at least one electrical conductor in a mould in the desired configuration for carrying electrical current when incorporated in the apparatus, introducing concrete into the mould so as to embed the electrical conductor in concrete so as to provide mechanical support for and electrical insulation of the conductor, and utilizing reinforcement means to permanently compressively stress the concrete, the stress applied to the concrete serving to minimize the effect of the differential in temperature coefficients of expansion between the concrete and the electrical conductor.

2. A method as claimed in claim I wherein the step of utilizing reinforcement means includes providing a plurality of reinforcement members which extend within said mould, tensioning said reinforcing members, pouring said concrete into said mould, and releasing the tension on said reinforcing members to provide said compressive stressing of the concrete.

3. A method as claimed in claim 1, wherein the reinforcement means is arranged so as to maintain the concrete under volume compression. I

4. A method as claimed in claim 1, wherein the reinforcement means comprises a vessel enclosing that portion of the electrical conductor which is to be supported in and insulated by concrete, the concrete being introduced into the vessel and pressurized, the pressure being maintained until the concrete has set.

5. A method as claimed in claim 1, wherein the reinforcement means comprises reinforcement members which extend through the mould and which are arranged to be tensioned so as to compressively stress the concrete when set.

6. A method as claimed in claim 5, wherein the compressive stress applied by the reinforcement members is parallel with the length of the electrical conductor.

7. A method of manufacturing an electromagnet in an electrical machine for accelerating charged particles, which method comprises supporting in a mould in the required relative locations a beam tube, magnet core laminations and electrical coil windings of uninsulated electrical conductor, embedding these components in concrete, and utilizing reinforcement means to permanently compressively stress the concrete so as to minimize the effects of the differential coefficient of expansion with temperature between the concrete and the electrical conductors. 

1. A method of manufacturing an electrical apparatus comprising supporting at least one electrical conductor in a mould in the desired configuration for carrying electrical current when incorporated in the apparatus, introducing concrete into the mould so as to embed the electrical conductor in concrete so as to provide mechanical support for and electrical insulation of the conductor, and utilizing reinforcement means to permanently compressively stress the concrete, the stress applied to the concrete serving to minimize the effect of the differential in temperature coefficients of expansion between the concrete and the electrical conductor.
 2. A method as claimed in claim 1 wherein the step of utilizing reinforcement means includes providing a plurality of reinforcement members which extend within said mould, tensioning said reinforcing members, pouring said concrete into said mould, and releasing the tension on said reinforcing members to provide said compressive stressing of the concrete.
 3. A method as claimed in claim 1, wherein the reinforcement means is arranged so as to maintain the concrete under volume compression.
 4. A method as claimed in claim 1, wherein the reinforcement means comprises a vessel enclosing that portion of the electrical conductor which is to be supported in and insulated by concrete, the concrete being introduced into the vessel and pressurized, the pressure being maintained until the concrete has set.
 5. A method as claimed in claim 1, wherein the reinforcement means comprises reinforcement members which extend through the mould and which are arranged to be tensioned so as to compressively stress the concrete when set.
 6. A method as claimed in claim 5, wherein the compressive stress applied by the reinforcement members is parallel with the length of the electrical conductor.
 7. A method of manufacturing an electromagnet in an electrical machine for accelerating charged particles, which method comprises supporting in a mould in the required relative locations a beam tube, magnet core laminations and electrical coil windings of uninsulated electrical conductor, embedding these components in concrete, and utilizing reinforcement means to permanently compressively stress the concrete so as to minimize the effects of the differential coefficient of expansion with temperature between the concrete and the electrical conductors. 